The present invention relates to mass fluid flow devices and methods of reducing contaminant, fluid ingress into mass fluid flow sensors.
Internal combustion engines today include electronic controls to provide a desired engine operation. Typically, the electronic control systems include a primary control unit for processing control algorithms and a variety of sensors for providing control signals to the primary control unit. One sensor for achieving a desired engine control is a mass fluid flow sensor, e.g., a mass air flow sensor, for measuring air intake into an internal combustion engine. Typically, a mass fluid flow sensor includes a printed circuit board disposed therein for determining fluid flow within a vehicle.
The mass fluid flow measurement should be accurate in order to provide a desired engine operation. One problem that manufacturers have experienced is related to reducing contaminant fluids from ingressing and contacting conductive material of the printed circuit boards in the mass fluid flow sensors. For example, it has been found that rubber hoses used in vehicles are outgassing sulfur and sulfur compounds. The sulfur becomes airborne and may react with copper and silver. When sulfur reacts with aluminum, for example, aluminum sulfide is formed. It is known that aluminum sulfide has a resistive characteristic and is not conductive. However, both aluminum and silver are materials used on thick film substrates for printed circuit boards or circuit modules. Thus, in many situations, sulfur which ingresses and contacts aluminum, for example, of a printed circuit board may result in the formation of aluminum sulfide. Thus, in such a situation, the printed circuit board may be undesirably altered or shorted when aluminum sulfide is formed thereon.
In these situations, outgassed sulfur typically ingresses into the mass fluid flow sensor through a seal between two materials, for example, metal and plastic. This may occur after the seal has experienced conditions of fluctuating temperatures wherein thermal expansions have occurred between the materials of the seal. Moreover, the adhesive used to seal the materials may have degraded, reducing its sealing properties to allow contaminants such as sulfur to ingress therethrough.
Thus, it is an aspect of one embodiment of the present invention to provide a mass air flow device having reduced contaminant ingress therethrough.
It is another aspect of the present invention to provide a method of reducing contaminant fluid ingress into the device to reduce corrosion of a printed circuit board within the device.
It is yet another aspect of the present invention to provide a device for detecting a condition of a flowing fluid within a vehicle. The device comprises a base plate having a receiving surface and a circumferential edge. The base plate is made of a first material having a first coefficient of thermal expansion. The device further includes a substrate having a printed circuit, wherein the substrate is disposed on the receiving surface of the base plate.
The device further includes a housing including a cover and peripheral side walls extending therefrom. The side walls attach to the receiving the surface adjacent the circumferential edge to define a peripheral interface enclosing the substrate within the housing. The housing is made of a second material having a second coefficient of thermal expansion. The device further includes an adhesive material disposed at the interface between the circumferential edge and the peripheral side walls to adhere the housing to the base plate. The adhesive material has a predetermined thermal expansion coefficient and a predetermined elastic modulus to reduce fluid ingress through the interface and to accommodate thermal expansions of the first and second materials.
Further aspects, features and advantages of the invention will become apparent from consideration of the following description and the appended claims when taken in connection with the accompanying drawings.